[RFC] Issue #3603 Fix - Should we do more?

Over the early part of this year Mike Pilato and other Collabnet
employees met with many of our customers to get feeback on Subversion,
see http://svn.apache.org/repos/asf/subversion/trunk/notes/feedback/cmpilato-user-calls

One merge related item that came up was: '--reintegration should
tolerate sparse checkouts that aren't affected'.

I created issue #3603 to track this.

The good news is that simply removing the check for a sparse WC works
perfectly in the case where the 'missing' subtrees in the reintegrate
target are unaffected by the merge: The merge succeeds, no new subtree
mergeinfo is created, no errors, it just DTRT.

If the reintegrate target is missing a subtree that *is* affected by
the merge, then a tree-conflict occurs. Subtree mergeinfo is also set
to partition the missing subtree so it doesn't inherit the mergeinfo
set on the root (exactly like a non-reintegrate merge does already).

My question is this: Is that sufficient?

I think it is. It's not as if reintegrate merges can't result in tree
conflicts already (e.g. if work continues on trunk after the last sync
merge to a branch, the reintegration of the branch back to trunk can
easily cause this).

In a perfect world maybe we'd give a error along the lines of 'hey,
you are trying to reintegrate into a shallow WC and some of the paths
affected by the merge aren't present, you are going to get tree
conflicts, is this really what you want? :-)'

But going this route adds more merge special casing and obviously has
a performance penalty, two things we definitely don't need more of. I
think that if you are reintegrating into a shallow WC we should simply
permit it and assume this this is what you really want. Anyone
disagree? If not, I'll be applying the attached patch RSN.

[[[
Fix issue #3603 'allow reintegrate merges into WCs with missing subtrees'.

* subversion/libsvn_client/merge.c

  (ensure_wc_reflects_repository_subtree): Consider shallow WCs as ready
   to reintegrate to. That's it! Nothing special, it works as you'd
   expect.

* subversion/tests/cmdline/merge_tests.py

  (reintegrate_fail_on_shallow_wc): Rename to...

  (reintegrate_on_shallow_wc): ...this. Reimplement the test to expect
   success when reintegrating into a shallow WC.

  (test_list): Reflect test rename.

]]]

Paul